U.S. patent application number 14/449811 was filed with the patent office on 2014-11-20 for forming structures using aerosol jet .rtm. deposition.
The applicant listed for this patent is Optomec, Inc.. Invention is credited to Bruce H. King, Jason A. Paulsen, Michael J. Renn.
Application Number | 20140342082 14/449811 |
Document ID | / |
Family ID | 36588543 |
Filed Date | 2014-11-20 |
United States Patent
Application |
20140342082 |
Kind Code |
A1 |
Renn; Michael J. ; et
al. |
November 20, 2014 |
Forming Structures Using Aerosol Jet .RTM. Deposition
Abstract
Method and apparatus for direct writing of passive structures
having a tolerance of 5% or less in one or more physical,
electrical, chemical, or optical properties. The present apparatus
is capable of extended deposition times. The apparatus may be
configured for unassisted operation and uses sensors and feedback
loops to detect physical characteristics of the system to identify
and maintain optimum process parameters.
Inventors: |
Renn; Michael J.; (Hudson,
WI) ; King; Bruce H.; (Albuquerque, NM) ;
Paulsen; Jason A.; (Cedar Rapids, IA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Optomec, Inc. |
Albuquerque |
NM |
US |
|
|
Family ID: |
36588543 |
Appl. No.: |
14/449811 |
Filed: |
August 1, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12720573 |
Mar 9, 2010 |
8796146 |
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14449811 |
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11302481 |
Dec 12, 2005 |
7674671 |
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12720573 |
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60635848 |
Dec 13, 2004 |
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Current U.S.
Class: |
427/79 ; 264/104;
264/261; 427/101; 427/421.1; 427/58 |
Current CPC
Class: |
B05D 1/02 20130101; H01L
21/76802 20130101; H01L 21/76879 20130101; H01C 17/06 20130101;
H01L 21/76805 20130101; H01L 41/314 20130101; H01B 13/0026
20130101; H01L 21/76804 20130101; H01C 17/08 20130101; H01L
21/76877 20130101 |
Class at
Publication: |
427/79 ;
427/421.1; 427/58; 427/101; 264/261; 264/104 |
International
Class: |
B05D 1/02 20060101
B05D001/02; H01B 13/00 20060101 H01B013/00 |
Claims
1. A method of changing a property of a structure, the method
comprising the step of depositing an aerosol comprising a material
on or adjacent to a structure.
2. The method of claim 1 wherein the depositing step comprises
depositing the material between two portions of the structure.
3. The method of claim 1 wherein the deposited material changes the
cross-sectional area of the deposit, the surface area of the
deposit, or the length of the deposit.
4. The method of claim 1 wherein the property is selected from the
group consisting of electrical resistance, resistivity,
conductivity, electrical conductance, inductance, capacitance,
refractive index, etch resistance, a physical property, a thermal
property, an optical property, an electrical property, and a
chemical property.
5. A method of depositing a via, the method comprising the steps
of: aerosolizing a material; and depositing the material so that it
electrically connects at least two layers of a circuit; wherein the
material forms a passive via.
6. The method of claim 5 wherein the passive via comprises a
resistive element or a capacitive element.
7. The method of claim 5 wherein the passive via is oriented
substantially perpendicular to the layers.
8. The method of claim 5 wherein the material is deposited into a
hole.
9. A method of coating an inside surface of a via, the method
comprising the steps of: aerosolizing a liquid suspension of a
material; filling a first hole with the liquid; drying the liquid;
and adhering the material to the inside surface of the first hole;
and the adhered material forming a second hole.
10. The method of claim 9 wherein the inside surface comprises the
bottom of the hole and the walls of the hole.
11. The method of claim 9 wherein the second hole is smaller than
the first hole.
12. The method of claim 9 wherein the second hole is within the
first hole.
13. The method of claim 12 wherein the second hole is approximately
the same shape as the first hole.
14. The method of claim 9 wherein the first hole, the material, and
the second hole form a via.
15. The method of claim 14 wherein the material is highly
conductive.
16. The method of claim 15 further comprising the step of flowing
electrical current through the material along the walls of the via.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 12/720,573, entitled "Aerodynamic Jetting of
Blended Aerosolized Materials", filed on Mar. 9, 2010, issuing on
Aug. 5, 2014 as U.S. Pat. No. 8,796,146, which application is a
continuation application of U.S. patent application Ser. No.
11/302,481, entitled "Aerodynamic Jetting of Aerosolized Fluids for
Fabrication of Passive Structures", filed on Dec. 12, 2005, which
issued as U.S. Pat. No. 7,674,671, which application claims the
benefit of the filing of U.S. Provisional Patent Application Ser.
No. 60/635,848, entitled "Solution-Based Aerosol Jetting of Passive
Electronic Structures" filed on Dec. 13, 2004. The specification
and claims of these applications are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention (Technical Field)
[0003] The present invention relates generally to the field of
direct deposition of passive structures. More specifically, the
invention relates to the field of maskless, precision deposition of
mesoscale passive structures onto planar or non-planar targets,
with an emphasis on deposition of precision resistive
structures.
[0004] 2. Background Art
[0005] Note that the following discussion refers to a number of
publications and references. Discussion of such publications herein
is given for more complete background of the scientific principles
and is not to be construed as an admission that such publications
are prior art for patentability determination purposes.
[0006] Various methods for deposition of passive structures exist,
however, thick film and thin film methods have played a dominant
role in the deposition of passive structures, including but not
limited to resistors or capacitors, onto various electronic and
microelectronic targets. By way of example, the thick film
technique typically uses a screen-printing process to deposit
electronic pastes with linewidths as small as 100 microns. Thin
film methods for the printing of electronic structures include
vapor deposition techniques, such as chemical vapor deposition and
laser-assisted chemical vapor deposition, as well as physical
deposition techniques, such as sputtering and evaporation.
[0007] U.S. Pat. No. 4,938,997 discloses a method for the
fabrication of thick film resistors on ceramic substrates, with
tolerances consistent with those required for microelectronic
circuitry. In this method, a ruthenium-based resistor material is
screen printed onto the substrate and fired at temperatures in
excess of 850.degree. C. U.S. Pat. No. 6,709,944 discloses a method
for fabrication of passive structures on flexible substrates by
using ion bombardment to activate the surface of a substrate such
as polyimide, forming a graphite-like carbon region that may be
combined with another deposited material--such as titanium--to form
a passive structure. U.S. Pat. No. 6,713,399 discloses a method for
the fabrication of embedded resistors on printed circuit boards.
The method uses a thin film process to form embedded passive
structures in recesses that have been formed in a conductive layer.
The method of U.S. Pat. No. 6,713,399 discloses a process that
eliminates the high resistance variation seen in polymer thick film
embedded resistors.
[0008] While thick film and thin film methods of passive structure
fabrication are well-developed, these processes may be unsuitable
for certain deposition applications. Some disadvantages of thick
film processes are the relatively large minimum linewidths that are
characteristic of the technique, the need for mask utilization, and
the need for high-temperature processing of the deposited material.
The disadvantages of typical thin film processes include the need
to use masks, vacuum atmospheres, and multi-step photolithographic
processes.
[0009] In contrast with conventional methods for deposition of
passive structures, the M.sup.3D.RTM. process is a direct printing
technique that does not require the use of vacuum chambers, masks,
or extensive post-deposition processing. Commonly-owned
International Patent Application Number PCT/US01/14841, published
as WO 02/04698 and incorporated herein by reference, discloses a
method for using an aerosol jet to deposit passive structures onto
various targets, but gives no provision for lowering the tolerance
of deposited structures to levels that are acceptable for
manufacturing of electronic components. Indeed, the use of a
virtual impactor in the invention disclosed therein eventually
leads to failure of the system due to the accumulation of particles
in the interior of the device. As a result, the maximum runtime
before failure of the previously disclosed system is 15 to 100
minutes, with the electrical tolerances of deposited structures of
approximately 10% to 30%.
[0010] Contrastingly, the present invention can deposit passive
structures with conductance, resistance, capacitance, or inductance
values with tolerances of less than 5%, and runtimes of several
hours.
SUMMARY OF THE INVENTION
[0011] The present invention is an apparatus for depositing a
passive structure comprising a material on a target, the apparatus
comprising an atomizer for forming an aerosol comprising the
material and a carrier gas, an exhaust flow controller for
exhausting excess carrier gas, a deposition head for entraining the
aerosol in a cylindrical sheath gas flow, a pressure sensing
transducer, a cross connecting the atomizer, the deposition head,
the exhaust flow controller, and the transducer, wherein the
tolerance of a desired property of the passive structure is better
than approximately 5%. The deposition head and atomizer are
preferably connected to the cross at inlets opposite each other.
The exhaust flow controller preferably exhausts excess carrier gas
at a direction perpendicular to an aerosol direction of travel
through the cross. The exhaust flow controller preferably reduces
the carrier gas flowrate.
[0012] The apparatus preferably further comprises a processor for
receiving data from the transducer, the processor determining if a
leak or clog is present in the apparatus. In such case the
apparatus preferably further comprises a feedback loop for
automatically purging the apparatus if a clog is detected or
automatically ceasing operation of the apparatus if a leak is
detected. The apparatus preferably further comprises a laser whose
beam passes through the flowing aerosol and a photodiode for
detecting scattered light from the laser. The laser beam is
preferably perpendicular to the flow direction of the aerosol and
the photodiode is preferably oriented orthogonally to both the
laser beam and the flow direction. The photodiode is preferably
connected to a controller for automatically controlling the
atomizer power.
[0013] The invention is also a method of depositing a passive
structure comprising a material on a target, the method comprising
the steps of: atomizing the material; entraining the atomized
material in a carrier gas to form an aerosol; removing excess
carrier gas from the aerosol via an opening oriented
perpendicularly to a flow direction of the aerosol; monitoring a
pressure of said aerosol; surrounding the aerosol with a sheath
gas; and depositing the material on the target; wherein a tolerance
of a desired property of the passive structure is better than
approximately 5%. The method preferably further comprises the steps
of determining the existence of a leak or clog based on a value of
the pressure, and automatically purging the system if a clog exists
or automatically ceasing operation if a leak exists. The method
preferably further comprises the steps of shining a laser beam into
the aerosol and measuring scattered light from the laser beam. The
measuring step is preferably performed by a detector oriented
orthogonally to both the laser beam and a flow direction of the
aerosol. The method preferably further comprises the step of
varying the power used in the atomizing step based on an amount of
scattered light detected in the measuring step.
[0014] The method preferably further comprises the step of
processing the material, the processing step preferably selected
from the group consisting of humidifying the aerosol, drying the
aerosol, heating the aerosol, heating the deposited material,
irradiating the deposited material with a laser beam, and
combinations thereof. Irradiating the deposited material with a
laser beam preferably enables a linewidth of the deposited material
to be as low as approximately 1 micron. Irradiating the deposited
material with a laser beam preferably does not raise an average
temperature of the target to above a damage threshold.
[0015] An object of the present invention is to pre-process a
material in flight and/or post processing treatment the material
after its deposition on a target resulting in a physical and/or
electrical property having a value near that of a bulk
material.
[0016] Another object of the present invention is to provide a
deposition apparatus which is capable of long runtimes.
[0017] An advantage of the present invention is that deposited
passive structures have conductance, resistance, capacitance, or
inductance values with tolerances of less than 5%.
[0018] Other objects, advantages and novel features, and further
scope of applicability of the present invention will be set forth
in part in the detailed description to follow, taken in conjunction
with the accompanying drawings, and in part will become apparent to
those skilled in the art upon examination of the following, or may
be learned by practice of the invention. The objects and advantages
of the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the
appended claims.
A BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate several embodiments of
the present invention and, together with the description, serve to
explain the principles of the invention. The drawings are only for
the purpose of illustrating a preferred embodiment of the invention
and are not to be construed as limiting the invention. In the
drawings:
[0020] FIG. 1a is a schematic of the embodiment of the preferred
M.sup.3D.RTM. apparatus of the present invention capable of
extended runtimes and depositing passive structures with tolerances
below 5%.
[0021] FIG. 1b shows the general embodiment of the preferred
M.sup.3D.RTM. apparatus of the present invention, configured for
pneumatic atomization.
[0022] FIG. 2 is a graph showing the relationship between sheath
gas pressure and total gas flow rate.
[0023] FIG. 3a is a schematic of a cross section of a passive
structure with terminations. The height of the structure is
t.sub.1.
[0024] FIG. 3b is a schematic of FIG. 3a, with an additively
trimmed passive structure. The height of the structure is t.sub.2,
where t.sub.2>t.sub.1.
[0025] FIG. 4 is a schematic showing that the rightmost resistor
has a greater resistance than the middle structure, by virtue of
the greater length of resistor material between the pads.
[0026] FIG. 5a is a schematic of a ladder resistor prior to direct
write of additional passive structures.
[0027] FIG. 5b is a schematic of a ladder resistor showing how
structures can be added after the board has been processed and
populated with other components, thereby tuning a circuit after it
is mostly complete.
[0028] FIG. 6 is a schematic of a passive structure written over
the edge of a target.
[0029] FIG. 7a is a schematic of a linear passive trace with
terminated resistors.
[0030] FIG. 7b is a schematic of a serpentine passive trace with
terminated resistors.
[0031] FIG. 8 is a schematic of a resistor embedded in a via
between two circuit layers.
[0032] FIG. 9 depicts a method for depositing a coating on the
walls and bottom of a via.
[0033] FIGS. 10a-c are schematics using the M.sup.3D.RTM. process
in a hybrid additive/subtractive technique to fabricate precision
metal structures using an etch resist.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Best Modes for Carrying Out the Invention
Introduction and General Description
[0034] The M.sup.3D.RTM. process is an additive direct printing
technology that operates in an ambient environment, and eliminates
the need for lithographic or vacuum deposition techniques. The
method is capable of depositing a passive electronic component in a
predetermined pattern, and uses aerodynamic focusing of an aerosol
stream to deposit patterns onto a planar or non-planar target
without the use of masks or modified environments. The
M.sup.3D.RTM. method is compatible with commercial thick film and
polymer thick film paste compositions, and may also be used with
liquid precursor-based formulations, particle-based formulations,
and formulations consisting of a combination of particles and
liquid precursors. The method is also capable of depositing
multiple formulations onto the same target layer. This capability
enables direct deposition of resistive structures with a large
range of resistance values--ranging from under 50 .OMEGA./square to
over 500 K.OMEGA./square--onto the same layer.
[0035] The M.sup.3D.RTM. method is capable of blending different
formulations, for example one low-value and one high-value
composition, in-transit, in a method in which multiple atomizers
are preferably used to aerosolize the two compositions. The
formulations are preferably deposited through a single deposition
head, and blending may occur during aerosol transport, or when the
aerosol droplets combine on the target. This method allows for
automated tailoring of a formulation, allowing for the resistivity,
or other electrical, thermal, optical, or chemical property of the
deposit, to be continuously varied from the low value to the high
value. The blending process can also be applied to pastes, inks,
various fluids (including, but not limited to, chemical precursor
solutions, particle suspensions of electronic, optical, biological
and bio-compatible materials, adhesives), and combinations
thereof.
[0036] As used throughout the specification and claims, "passive
structure" means a structure having a desired electrical, magnetic,
or other property, including but not limited to a conductor,
resistor, capacitor, inductor, insulator, dielectric, suppressor,
filter, varistor, ferromagnet, adhesive, and the like.
[0037] The M.sup.3D.TM. process preferably deposits material in an
aerosolized form. Aerosolization of most particle suspensions is
peferably performed using a pneumatic device, such as a nebulizer,
however ultrasonic aerosolization may be used for particle
suspensions consisting of small particles or low-density particles.
In this case, the solid particles may be suspended in water or an
organic solvent and additives that maintain the suspension. The two
atomization methods allow for the generation of droplets or
droplet/particles with sizes typically in, but not limited to, the
1-5 micron size range.
[0038] Ultrasonically aerosolized compositions typically have
viscosities ranging from 1-10 cP. Precursor and precursor/particle
compositions typically have viscosities of 10-100 cP, and are
preferably aerosolized pneumatically. Compositions with viscosities
of 100-1000 cP are also preferably pneumatically aerosolized. Using
a suitable diluent, compositions with viscosities greater than 1000
cP may be modified to a viscosity suitable for pneumatic
aerosolization.
[0039] The preferred apparatus of the present invention, which is
capable of depositing passive structures having tolerances below 5%
with extended runtimes, is shown in FIG. 1a. FIG. 1b shows the
M.sup.3D.RTM. apparatus configured for pneumatic atomization, and
details the most general embodiment of the apparatus. An inert
carrier gas or carrier fluid is preferably used to deliver the
aerosolized sample to the deposition module. In the case of
ultrasonic atomization, the aerosol-laden carrier gas preferably
enters the deposition head immediately after the aerosolization
process. The carrier gas may comprise compressed air, an inert gas
(which may comprise a solvent vapor), or a mixture of both. The
pneumatic aerosolization process requires a carrier gas flow rate
that preferably exceeds the maximum allowable gas flow rate through
deposition head 22. To enable the use of large carrier gas flow
rates (for example, approximately 0.2 to 2 liter/min), a virtual
impactor is preferably used to reduce the flowrate of the carrier
gas, without appreciable loss of particles or droplets. The number
of stages used in the virtual impactor may vary, and is dependent
on the amount of carrier gas that must be removed. The stream is
introduced into the M.sup.3D.RTM. deposition head, where an annular
flow is developed, consisting of an inner aerosol stream surrounded
by a sheath gas. The co-flowing configuration is capable of
focusing the aerosol stream to approximately one-tenth the size of
the orifice diameter.
[0040] When fabricating passive structures using an annular flow,
the aerosol stream preferably enters through ports mounted on
deposition head 22 and is directed towards the orifice. Aerosol
carrier gas flow controller 10 preferably controls the mass
throughput. Inside the deposition head, the aerosol stream is
preferably initially collimated by passing through a
millimeter-size orifice. The emergent particle stream is then
combined with a sheath gas or fluid, forming an annular
distribution consisting of an inner aerosol-laden carrier gas and
an outer sheath gas or fluid. The sheath gas most commonly
comprises compressed air or an inert gas, where one or both may
contain a modified solvent vapor content. The sheath gas enters
through the sheath air inlet below the aerosol inlet and forms an
annular flow with the aerosol stream. Gas flow controller 12
preferably controls the sheath gas. The combined streams exit the
chamber through an orifice directed at target 28. This annular flow
focuses the aerosol stream onto target 28 and allows for deposition
of features with dimensions as small as 10 microns or lower. The
purpose of the sheath gas is to form a boundary layer that both
focuses the aerosol stream and prevents particles from depositing
onto the orifice wall. This shielding effect minimizes clogging of
the orifices.
[0041] The diameter of the emerging stream (and therefore the
linewidth of the deposit) is controlled by the orifice size, the
ratio of sheath gas flow rate to carrier gas flow rate, and the
spacing between the orifice and target 28. In a typical
configuration, target 28 is attached to a platen that moves in two
orthogonal directions under computer control via X-Y linear stages,
so that intricate geometries may be deposited. An alternate
configuration allows for deposition head 22 to move in two
orthogonal directions while maintaining target 28 in a fixed
position. Yet another configuration allows for movement of
deposition head 22 in one direction, while target 28 moves in a
direction orthogonal to that of deposition head 22. The process
also enables the deposition of three-dimensional structures.
[0042] In the M.sup.3D.RTM. method, once the sheath gas is combined
with the aerosol stream, the flow does not need to pass through
more than one orifice in order to deposit sub-millimeter
linewidths. In the deposition of a 10-micron line, the
M.sup.3D.RTM. method typically achieves a flow diameter
constriction of approximately 250, and may be capable of
constrictions in excess of 1000, for this "single-stage"
deposition. No axial constrictors are used, and the flows typically
do not reach supersonic flow velocities, thus preventing the
formation of turbulent flow, which could potentially lead to a
complete constriction of the flow.
Aerosolization and Virtual Impaction
[0043] In the preferred operation of the system of the present
invention detailed in FIG. 1a, Collison-type pneumatic atomizer 32
aerosolizes the material in the sample vial. The aerosol-laden gas
stream is delivered to cross 30 that bridges atomizer 32,
deposition head 22, exhaust flow controller 34, and pressure
sensing transducer 36. Cross 30 is preferably configured so that
the aerosol flow inlet is opposite the aerosol flow outlet. The
outlet is connected to the M.sup.3D.RTM. deposition head. Excess
carrier gas is preferably exhausted from the system 90.degree. from
the aerosol inlet/outlet line of travel. Mass flow controller 34 is
preferably used to control the amount of gas that is exhausted from
the system. Controlling the exhaust flow using a flow controller
increases the precision of the deposition process by aiding in the
control of the mass flux of the material that passes to the
deposition head.
[0044] In an alternative embodiment, the atomizer is located
directly adjacent to the virtual impactor. Positioning the virtual
impactor near the pneumatic atomizer output results in the
deposition of larger droplets, since the aerosol ultimately spends
less time in transit from the atomizer to the target, and undergoes
reduced evaporation. The deposition of larger droplets can produce
a considerable effect on the characteristics of the deposited
structure. In general, deposited structures formed from larger
droplets show less particle overspray and improved edge definition
when compared with structures deposited with small to moderate size
droplets. The atomizer is optionally agitated to prevent material
agglomeration.
[0045] Typically the carrier gas flowrate needed for pneumatic
atomization must be reduced after the aerosol is generated, in
order for the aerosol stream to be introduced into the deposition
head. The required reduction in carrier gas flowrate--from as much
as 2 L/min to as little as 10 ml/min--is preferably accomplished
using a virtual impactor. However, the use of a virtual impactor
may cause the system to be prone to clogging, decreasing the
operating time of the apparatus to as little as several minutes,
while undesirably decreasing the tolerance of the deposited
structure. For example, the apparatus of FIG. 1b may deposit
carbon-based resistors for as little as 15 minutes before failure,
with a tolerance in the resistance values of as much as 30%. The
apparatus of FIG. 1a, contrastingly, replaces the standard
M.sup.3D.RTM. virtual impactor with cross 30 that exhausts excess
carrier gas from the system, while minimizing the loss of particles
and buildup of particles with the system. Cross 30 acts as a
virtual impactor with considerably larger jet and collector orifice
diameters than those used with the standard impactor. The use of
larger jet and collector orifice diameters may increase the amount
of material that flows through the virtual impactor minor flow
axis, while minimizing the accumulation of material on the interior
of the device.
Leak/Clog Sensor
[0046] The present invention preferably uses a leak/clog sensor
comprising pressure transducers to monitor the pressure developed
at the atomizer gas inlet and at the sheath gas inlet. In normal
operation, the pressure developed within the system is related to
the total gas flow rate through the system, and can be calculated
using a second-order polynomial equation. A plot of pressure versus
total flow through the system is shown in FIG. 2. If the system
pressure is higher than the pressure predicted by the curve of FIG.
2, a non-ideal flow may have developed within the system as a
result of material accumulation. If the pressure is too low, a
system leak is present, and material deposition may be inhibited or
stopped entirely. The second order polynomial equation of the curve
representing normal operation is of the form:
P=M.sub.0+M.sub.1Q+M.sub.2Q.sup.2
where P is the sheath gas pressure and Q is the total flow rate.
The total flow rate through the system is given by:
Q.sub.ultrasonic=F.sub.sheath+F.sub.ultrasonic
Q.sub.pneumatic=F.sub.sheath+F.sub.pneumatic-F.sub.exhaust
where F is the device flow rate. The coefficients M.sub.0, M.sub.1,
and M.sub.2 are constants for each deposition tip diameter, but are
variable with respect to atmospheric pressure.
[0047] The leak/clog sensor provides a valuable system diagnostic
that can allow for continuous manual or automated monitoring and
control of the system. When operating in an unassisted mode, the
system may be monitored for clogs, and automatically purged when an
increase in pressure beyond a pre-determined value is detected.
Mist Sensing
[0048] Quantitative measurement of the amount of aerosol generated
by the atomizer units is critical for extended manual or automated
operation of the M.sup.3D.RTM. system. Maintenance of a constant
mist density allows for precision deposition, since the mass flux
of aerosolized material delivered to the target can be monitored
and controlled.
[0049] The system of the present invention preferably utilizes a
mist sensor, which preferably comprises a visible wavelength laser
whose beam passed through the aerosol outlet tube of the atomizer
unit. The beam is preferably oriented perpendicular to the axis of
the tube, and silicon photodiodes are preferably positioned
adjacent to the tube on an axis perpendicular to both the axes of
the tube and the laser. As the laser interacts with the mist
flowing through the tube, light is scattered through a wide angle.
The energy detected by the photodiodes is proportional to the
aerosol density of the mist flow. As the mist flow rate increases,
the photodiode output increases until a state of saturation is
reached, at which the photodiode output becomes constant. A
saturated mist level condition is preferred for constant mist
output, so that a constant photodiode output indicates an optimum
operating condition.
[0050] In a feedback control loop, the output of the photodiodes is
monitored and can be used to determine the input power to the
ultrasonic atomizer transducer.
Processing The aerosolized material compositions may be processed
in-flight--during transport to the deposition head 22
(pre-processing)--or once deposited on the target 28
(post-processing). Pre-processing may include, but is not limited
to, humidifying or drying the aerosol carrier gas or the sheath
gas. The humidification process may be accomplished by introducing
aerosolized droplets and/or vapor into the carrier gas flow. The
evaporation process is preferably accomplished using a heating
assembly to evaporate one or more of the solvent and additives.
[0051] Post-processing may include, but is not limited to using one
or a combination of the following processes: (1) thermally heating
the deposited feature, (2) subjecting the deposited feature to a
reduced pressure atmosphere, or (3) irradiating the feature with
electromagnetic radiation. Post-processing of passive structures
generally requires temperatures ranging from approximately 25 to
1000 .degree. C. Deposits requiring solvent evaporation or
cross-linking are typically processed at temperatures of
approximately 25 to 250.degree. C. Precursor or nanoparticle-based
deposits typically require processing temperatures of approximately
75 to 600.degree. C., while commercial fireable pastes require more
conventional firing temperatures of approximately 450 to
1000.degree. C. Commercial polymer thick film pastes are typically
processed at temperatures of approximately 25.degree. to
250.degree. C. Post-processing may optionally take place in an
oxidizing environment or a reducing environment. Subjecting the
deposit to a reduced pressure environment before or during the
heating step, in order to aid in the removal of solvents and other
volatile additives, may facilitate processing of passive structures
on heat-sensitive targets.
[0052] Two preferred methods of reaching the required processing
temperatures are by heating the deposit and target on a heated
platen or in a furnace (thermal processing), or by irradiating the
feature with laser radiation. Laser heating of the deposit allows
for densification of traditional thick film pastes on
heat-sensitive targets. Laser photochemical processing has also
been used to decompose liquid precursors to form mid to high-range
resistors, low to mid-range dielectric films, and highly conductive
metal. Laser processing may optionally be performed simultaneously
with deposition. Simultaneous deposition and processing can be used
to deposit structures with thicknesses greater than several
microns, or to build three-dimensional structures. More details on
laser processing may be found in commonly-owned U.S. patent
application Ser. No. 10/952,108, entitled "Laser Processing For
Heat-Sensitive Mesoscale Deposition", filed on Sep. 27, 2004, the
specification and claims of which are incorporated herein by
reference.
[0053] Thermally processed structures have linewidths that are
partially determined by the deposition head and the deposition
parameters, and have a minimum linewidth of approximately 5
microns. The maximum single pass linewidth is approximately 200
microns. Linewidths greater than 200 microns may be obtained using
a rastered deposition technique. Laser-processed lines may have
linewidths ranging from approximately 1 to 100 microns (for a
structure deposited with a single pass). Linewidths greater than
100 microns may be obtained using a rastered processing technique.
In general, laser processing is used to densify or to convert films
deposited on heat-sensitive targets, such as those with low
temperature thresholds of 400.degree. C. or less, or when a
linewidth of less than approximately 5 microns is desired.
Deposition of the aerosol stream and processing may occur
simultaneously.
Types of Structures: Material Compositions
[0054] The present invention provides a method for precision
fabrication of passive structures, wherein the material composition
includes, but is not limited to, liquid chemical precursors, inks,
pastes, or any combination thereof. Specifically, the present
invention can deposit electronic materials including but not
limited to conductors, resistors, dielectrics, and ferromagnetic
materials. Metal systems include, but are not limited to, silver,
copper, gold, platinum, and palladium, which may be in commercially
available paste form. Resistor compositions include, but are not
limited to, systems composed of silver/glass, ruthenates, polymer
thick films formulations, and carbon-based formulations.
Formulations for deposition of capacitive structures include, but
are not limited to, barium titanate, barium strontium titanate,
aluminum oxide, and tantalum oxide. Inductive structures have been
deposited using a manganese/zinc ferrite formulation blended with
low-melting temperature glass particles. The present invention can
also blend two uv-curable inks to produce a final composition with
a targeted characteristic, such as a specific refractive index.
[0055] A precursor is a chemical formulation consisting of a solute
or solutes dissolved in a suitable solvent. The system may also
contain additives that alter the fluid, chemical, physical, or
optical properties of the solution. Inks may be comprised of
particles, including but not limited to metal nanoparticles or
metal nanoparticles with glass inclusions, of an electronic
material suspended in a fluid medium. Depositable pastes include,
but are not limited to, commercially available paste formulations
for conductive, resistive, dielectric, and inductive systems. The
present invention can also deposit commercially available adhesive
pastes.
Resistors
[0056] A silver/glass resistor formulation may be composed of a
liquid molecular precursor for silver, along with a suspension of
glass particles, or silver and glass particles, or silver particles
in a liquid precursor for glass. A ruthenate system may be
comprised of conductive ruthenium oxide particles and insulating
glass particles, ruthenium oxide particles in a precursor for
glass, or a combination of a ruthenium oxide precursor and a
precursor for glass or an insulating medium. Precursor compositions
and some precursor/particle compositions may have viscosities of
approximately 10 to 100 cP, and may be aerosolized ultrasonically.
Resistor pastes may be comprised of either or both of ruthenates,
polymer thick film formulations, or carbon-based formulations.
Commercially available ruthenate pastes, typically consisting of
ruthenium oxide and glass particles, having viscosities of 1000 cP
or greater, may be diluted with a suitable solvent such as
terpineol to a viscosity of 1000 cP or less. Polymer thick film
pastes may also be diluted in a suitable solvent to a similar
viscosity, so that pneumatic aerosolization and flow-guidance is
enabled. Similarly, carbon-based pastes can be diluted with a
solvent such as butyl carbitol to a viscosity of approximately 1000
cP or less. Therefore, many commercial paste compositions with
viscosities greater than 1000 cP may be modified and deposited
using the M.sup.3D.RTM. process.
Resistors: Range of Resistance, Repeatability, and Temperature
Coefficient of Resistance
[0057] The resistive structures deposited using the M.sup.3D.RTM.
process may comprise a resistance spanning approximately six orders
of magnitude, from 1 ohm to 1 Mohm. This range of resistance values
may be obtained by depositing the appropriate material with the
appropriate geometrical cross-sectional area. The tolerance or
variance of the resistance values--defined as the ratio of the
difference in the resistance value of the highest and lowest
passive structure and the average resistance value, for a set of
deposits--may be as low as 2 percent. The temperature coefficient
of resistance (TCR) for Ag/glass and ruthenate structures may range
from approximately .+-.50 to .+-.100 ppm.
Geometry
[0058] The present method is capable of producing a specific
electronic, optical, physical, or chemical value of a structure by
controlling the geometry of the deposit. For example, properties of
a structure can be altered by controlling the cross-sectional area
of the structure, as shown in FIGS. 3a and 3b. Resistance values
may be altered by adding material to an existing trace, thereby
increasing the cross sectional area of the total trace, thus
decreasing the resistance value as material is added to the
existing trace. This method is analogous to commonly used laser
trimming methods, however material is added rather than removed.
The additively trimmed passive trace 38 is deposited onto the
existing passive trace 40. As a further example, a specific value
may be obtained by controlling the length of a deposited structure;
as shown in FIG. 4, the rightmost resistor has a greater resistance
than the middle structure, by virtue of the greater length of
resistor material between the contact pads. The method of the
present invention may also be used to add material to a set of
traces or between one or more sets of contact pads 42 connected to
a pre-existing electronic circuit, as shown in FIGS. 5a and 5b.
Ladder passive traces 44a-b are added to existing passive trace 40.
This method enables tuning of the circuit to a specific response or
characteristic value. The method is also capable of creating
passive structures between layers of circuitry by making passive
connections in vias, or by wrapping resistor material 46 around the
edge of circuit layers, as shown in FIG. 6.
[0059] The passive structures deposited using the M.sup.3D.RTM.
process of the present invention typically have linear geometries,
such as the linear passive trace 48 shown in FIG. 7a. Other
geometries include, but are not limited to, serpentine 50 (as shown
in FIG. 7b), spiral, and helical patterns. Linewidths of deposited
resistor material typically range from approximately 10 to 200
microns, but could be greater or lower. Linewidths greater than 200
microns may be obtained by depositing material in a rastered
fashion. The thickness of the deposited film may range from a few
hundred nanometers to several microns.
Via Filling
[0060] The M.sup.3D.RTM. process can be used to fill vias,
providing electrical interconnectivity between adjacent layers of
an electronic circuit. The present invention allows for the
precise, uniform deposition of an aerosolized material over an
extended period of time, for example into via holes.
[0061] FIG. 8 shows a resistive connection between different layers
of circuitry. Conductive layers in a PCB (printed circuit board)
are typically connected by metal vias, however, the M.sup.3D.RTM.
process also allows for deposition of resistive structures into
vias. The resistive via configuration is advantageous since, by
moving the layer resistors into vias, additional space is provided
on the surface of the circuit board layers.
[0062] FIG. 9 depicts a method for depositing a coating on the
walls and bottom of a via. In FIG. 9a, via 60 is completely filled
with ink 62 using the process of the present invention. As ink 62
dries, the solids 64 will adhere onto the walls and the bottom of
the via, leaving the middle of the via hollow, as shown in FIG. 9b.
Coating the wall with highly conductive material results in a very
useful structure, because most of the current in a via flows along
the wall and not through the middle.
Dielectrics
[0063] In the case of fabrication of dielectric structures, an ink
can be comprised of a precursor for an insulator, such as
polyimide, while a paste may be a formulation containing dielectric
particles and low melting temperature glass inclusions. The
precision deposition offered by the present invention is critical
to fabrication of high tolerance capacitors, since the thickness
and uniformity of a capacitive film determines the capacitance and
the performance of the capacitor. Low-k dielectric materials such
as glass and polyimide have been deposited for dielectric layers in
capacitor applications, and as insulation or passivation layers
deposited to isolate electronic components. Mid-k and high-k
dielectrics such as barium titanate can be deposited for capacitor
applications.
Etch Resist
[0064] The present embodiment of the M.sup.3D.RTM. process may be
used in a hybrid additive/subtractive technique to fabricate
precision metal structures using an etch resist. Etch resist 70 is
preferably atomized and deposited through the deposition head onto
metal layer 72, as shown in FIG. 10a. A subtractive technique, for
example etching, is then used to remove the exposed metal, FIG.
10b. In the last step, the etch resist is removed, leaving metal
structure 74 on the underlying substrate, FIG. 10c. The
additive/subtractive etch resist process can be used to deposit
reactive metals such as copper.
Targets
[0065] Targets suitable for direct write of passive structures
using the M.sup.3D.RTM. process include, but are not limited to,
polyimide, FR4, alumina, glass, zirconia, and silicon. Processing
of resistor formulations on polyimide, FR4, and other targets with
low temperature damage thresholds, i.e. damage thresholds of
approximately 400.degree. C. or less, generally requires laser
heating to obtain suitable densification. Laser photochemical
processing may be used to direct write mid to high range resistor
materials such as strontium ruthenate on polyimide.
Applications
[0066] Applications enabled by fabrication of passive structures
using the M.sup.3D.RTM. process include, but are not limited to,
direct write resistors for electronic circuits, heating elements,
thermistors, and strain gauges. The structures may be printed on
the more conventional high-temperature targets such as alumina and
zirconia, but may also be printed on heat-sensitive targets such as
polyimide and FR4. The M.sup.3D.RTM. process may also be used to
print embedded passive structures onto pre-existing circuit boards,
onto planar or non-planar surfaces, and into vias connecting
several layers of a three-dimensional electronic circuit. Other
applications include, but are not limited to, blending passive
element formulations to produce a deposited structure with a
specific physical, optical, electrical, or chemical property;
repair of passive structures on pre-populated circuit boards; and
deposition of passive structures onto pre-populated targets for the
purpose of altering the physical, optical, electrical, or chemical
performance of a system. The present invention enables the above
applications with tolerances in physical or electrical properties
of 5% or less.
[0067] Although the present invention has been described in detail
with reference to particular preferred and alternative embodiments,
persons possessing ordinary skill in the art to which this
invention pertains will appreciate that various modifications and
enhancements may be made without departing from the spirit and
scope of the Claims that follow, and that other embodiments can
achieve the same results. The various configurations that have been
disclosed above are intended to educate the reader about preferred
and alternative embodiments, and are not intended to constrain the
limits of the invention or the scope of the Claims. Variations and
modifications of the present invention will be obvious to those
skilled in the art and it is intended to cover all such
modifications and equivalents. The entire disclosures of all
patents and publications cited above are hereby incorporated by
reference.
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